While advances in medical treatments have contributed to the overall decrease in HIV- related opportunistic infections and deaths in youth, the prevalence of HIV in youth remains high. In this Phase I study, we will design, build, and test Plus Care, a mobile health (mMealth) application that can be used by HIV-positive youth and their case managers (CMs) to support prompt linkage to care. While an increasing number of mHealth applications focus on improving general access to HIV testing, resources, and education, a critical gap in innovation remains in tools designed to address the specific needs of HIV-positive youth. Plus Care addresses this gap by leveraging mobile technology to support short-term case management and long-term self-care for HIV- positive youth today. The application will be accessed through smartphones by patients and case managers (CM). The primary objective of this Phase I study will be to determine the feasibility and usability of our application and prepare for Phase II. We will accomplish this in three Specific Aims using qualitative methods. First, we will collect formative data from patients (n=5) and CMs (n=5) recruited from the Boston Children's Hospital HAPPENS HIV/AIDS program to assess user needs, refine a paper prototype, and identify barriers and facilitators to the deployment of Plus Care (sub study 1). Second, we will develop a customized, working prototype for each type of user-patients and CMs-using user-centered design methods. Third, we will test Plus Care's usability with patients (n=5) and CMs (n=5) (sub study 2) in individualized sessions. Results will inform a Phase II study, where we will develop and rigorously evaluate the efficacy and cost- effectiveness of an enhanced version of the application.